Aug. 30, 2006
Erica Hupp/Dwayne Brown
Headquarters, Washington
202-358-1237/1726
Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0474
RELEASE: 06-300
NASA, NOAA DATA INDICATE OZONE LAYER IS RECOVERING
A new study using NASA and National Oceanic and Atmospheric
Administration (NOAA) data finds consistent evidence that Earth's
ozone layer is on the mend.
A team led by Eun-Su Yang of the Georgia Institute of Technology,
Atlanta, analyzed 25 years of independent ozone observations at
different altitudes in Earth's stratosphere, which lies between six
and 31 miles above the surface. The observations were gathered from
balloons, ground-based instruments, NASA and NOAA satellites.
The stratosphere is Earth's second lowest atmospheric layer. It
contains approximately 90 percent of all atmospheric ozone. The
researchers concluded the Earth's protective ozone layer outside of
the polar regions stopped thinning around 1997. Ozone in these areas
declined steadily from 1979 to 1997.
The abundance of human-produced ozone-destroying gases such as
chlorofluorocarbons peaked at about the same time (1993 in the lowest
layer of the atmosphere, 1997 in the stratosphere). Such substances
were phased out after the 1987 international Montreal Protocol was
enacted.
To measure ozone at different altitudes in the stratosphere, the team
combined data from balloons and independent ground-based observing
networks with monthly averaged satellite data. The satellite data
came from five independent NASA and NOAA instruments.
Measurements were compared with computer predictions of ozone recovery
that considered actual measured variations in human-produced
ozone-destroying chemicals. The calculations took into account other
factors that can affect ozone levels, such as sunspot cycle behavior,
seasonal changes and stratospheric wind patterns.
"These results confirm the Montreal Protocol and its amendments have
succeeded in stopping the loss of ozone in the stratosphere," Yang
said. "At the current recovery rate, the atmospheric modeling
community's best estimates predict the global ozone layer could be
restored to 1980 levels — the time that scientists first
noticed the harmful effects human activities were having on
atmospheric ozone — some time in the middle of this century."
The researchers concluded approximately one half the observed ozone
change was in the region of the stratosphere above 11 miles and the
rest in the lower stratosphere from six to 11 miles. The researchers
attribute the ozone improvement above 11 miles almost entirely to the
Montreal Protocol.
"Scientists expected the Montreal Protocol to be working in the middle
and upper stratosphere and it is," said co-author Mike Newchurch of
the University of Alabama in Huntsville. "The real surprise of our
research was the degree of ozone recovery we found at lower
altitudes, below the middle stratosphere. There, ozone is improving
faster than we expected, and appears to be due to changes in
atmospheric wind patterns, the causes of which are not yet well
understood. Until the cause of the recent ozone increase in the
lowermost stratosphere is better understood, making high-accuracy
predictions of how the entire ozone layer will behave in the future
will remain an elusive goal. Continued careful observation and
modeling are required to understand how the ozone recovery process
will evolve."
"Our study is unique because it measures changes in the ozone layer at
all heights in the atmosphere, then compares the data with models as
well as observations from other instruments that measure variations
in the total amount of ozone in the atmosphere," said Ross Salawitch,
a senior research scientist at NASA's Jet Propulsion Laboratory,
Pasadena, Calif.
Results are published in the latest Journal of Geophysical Research.
For information about NASA and agency programs, visit:
http://www.nasa.gov/home
Other media contacts: Chris Rink, NASA's Langley Research Center,
Hampton, Va., 757-864-6786; Jane Sanders, Georgia Institute of
Technology, 404-894-2214; Nina Stickles, Hampton University, Va.,
757-727-5457; Anatta, NOAA, Boulder, Colo., 303-497-6288; Phil
Gentry, University of Alabama, 256-824-6420; Harvey Leifert, American
Geophysical Union, Washington, 202-777-7507.
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